1. Field of Invention
The present invention is directed to playing balls and more specifically to softballs and baseballs having a combination core made of a foamed thermoplastic resin and an outer winding of yarn which is saturated with a latex based adhesive. The invention also includes the method of producing these balls.
2. Discussion of the Prior Art
In the past, various constructions have been used in the production of softballs and baseballs in order to produce balls having the proper characteristics for the type of play in which they are to be used. For example, conventional softballs have normally included a center made of cork or kapok over which a yarn winding is applied consisting of cotton and synthetic yarn. The wound core is then encased by a two piece stitched cover which may be made of any number of vinyl or rubber materials, but traditionally has been made of leather.
In the case of baseballs, traditional balls of this type have normally included a small cork and rubber starter core about one inch in diameter which is "random wound" with wool or synthetic blends of yarn. A thin layer of cotton finishing yarn is then applied bringing the final core to proper size. A two piece cover is sewn on the core producing a finished ball. Obviously the size, weight,, balance, flight characteristics, durability, resilience and sound of the ball when batted, whether it is a softball or baseball, are determined by the various combinations of core compositions and windings.
Although conventional balls of the type described above have met with varying success, they each suffer from a number of substantial drawbacks. For example, due to the fact that the center core section is relatively soft and therefore easily compressible, the cores have a tendency to deform or flatten when the ball is struck, causing the winding to shift. The shifting of the winding throws the ball out of balance which further degrades the ball. Additionally, due to the shift in winding material, the prior art balls have a tendency to develop soft spots after extended use which causes erratic flight and inconsistent rebound. Various attempts to glue the windings to the center have not met with complete success especially with windings applied to the smooth surface of solid core balls.
Other drawbacks of the prior art balls, and particularly baseballs, is that the yarn wound cores absorb moisture especially during damp or wet playing conditions. Damp yarn causes increased weight, erratic flight, reduced rebound, premature softness and eventual shrinkage. Moreover, since the prior art baseballs are random wound using numerous blends of yarn, it is difficult to set tension on the threads during the winding process, thereby producing broad inconsistencies in size, weight, rebound and density.
In an attempt to overcome the deficiencies of conventional wound balls and in order to reduce the relatively high cost of manufacturing balls having a center and outer windings, manufacturers have begun making balls using a solid plastic core covered with a two-piece stitched cover. Game balls of this type are described in U.S. Pat. No. 4,211,407 as having a core which consists essentially of a single unwound spherical mass of ethylene vinyl acetate copolymer.
Although unwound solid cored balls of this type can be used, it has been found they are extremely hard, and with respect to softballs, are too lively. It has also been found that solid cored balls, due to their surface hardness, subject the outer cover to increased wear and stitching thread breakage. Another drawback encountered is that solid cored balls have a greater tendency to dent aluminum bats particularly when used in cool weather.
If the plastic core is made softer in order to prevent cover splitting and thread breakage, the sound when struck with the bat becomes muffled and no longer audible enough to satisfy the fielding player whose ear is tuned to the sharp sound of a regulation batted ball. This sound is important since the fielding player uses it to judge hit distance while fielding the ball. Moreover, solid cored plastic balls tend to deform if used above the youth level of play.